System for collecting carbon dioxide in flue gas

ABSTRACT

A system for collecting carbon dioxide in flue gas includes a stack that discharges flue gas discharged from an industrial facility to outside, a blower that is installed at the downstream side of the stack and draws the flue gas therein, a carbon-dioxide collecting device that collects carbon dioxide in the flue gas drawn in by the blower, and a gas flow sensor arranged near an exit side within the stack. A drawing amount of the flue gas by the blower to the carbon-dioxide collecting device is increased until an flow rate of the flue gas from the stack becomes zero in the gas flow sensor, and when the discharged amount of flue gas from the stack becomes zero, drawing in any more than that amount is stopped, and the carbon dioxide in the flue gas is collected while the flue gas is drawn in by a substantially constant amount.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. application Ser. No. 12/368,474 filed onFeb. 10, 2009, the entire contents of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system for collecting carbon dioxidein flue gas, capable of stably processing all the carbon dioxide in theflue gas discharged from an industrial facility such as a gas turbine, afurnace, or a boiler.

2. Description of the Related Art

Conventionally, to collect carbon dioxide in flue gas, for example, asystem is adopted when an amine-based absorbing solvent is used as a CO₂absorbing solvent to remove and collect CO₂ from flue gas; firstly, aprocess is performed to bring the CO₂ absorbing solvent into contactwith the flue gas in an absorption column, and thereafter the CO₂absorbing solvent that has absorbed CO₂ is heated in a regenerationcolumn; secondly, CO₂ is freed and the CO₂ absorbing solvent isregenerated, and circulated in the absorption column again, and finally,reused (for example, see Japanese Patent Application Laid-open No.H3-193116).

FIG. 9 is an example of a conventional system for collecting Co₂ in fluegas. As shown in FIG. 9, a conventional CO₂ collecting system 1000includes an flue gas cooling device 1004 that cools flue gas 1002containing CO₂ discharged from an industrial facility 1001 such as aboiler and a gas turbine by cooling water 1003, a CO₂ absorption column1006 that brings the flue gas 1002 containing cooled CO₂ into contactwith a CO₂ absorbing solvent 1005 absorbing CO₂ to remove the CO₂ fromthe flue gas 1002, and a regeneration column 1008 that releases the CO₂from a CO₂ absorbing solvent (rich solvent) 1007 absorbing the CO₂ toregenerate the CO₂ absorbing solvent. In this device, a regenerated CO₂absorbing solvent (lean solvent) 1009 from which the CO₂ is removed inthe regeneration column 1008 is recycled as the CO₂ absorbing solvent inthe CO₂ absorption column 1006. The CO₂ absorption column 1006 and theregeneration column 1008 configure a CO₂ collecting device 1030.

In a CO₂ collection method using the conventional CO₂ collecting device1030, the flue gas 1002 containing CO₂, discharged from the industrialfacility such as a boiler and a gas turbine, is firstly sent to the fluegas cooling device 1004 after pressure is raised by an flue gas fan1010, cooled by cooling water 1003, and thereafter sent to the CO₂absorption column 1006.

In the CO₂ absorption column 1006, the flue gas 1002 is countercurrentlycontacted with, for example, the CO₂ absorbing solvent 1005 based on anamine-based absorbent, and the CO₂ in the flue gas 1002 is absorbed inthe CO₂ absorbing solvent 1005 due to a chemical reaction(R—NH₂+H₂O+CO₂→R—NH₃HCO₃), and flue gas 1011 from which the CO₂ isremoved is released from the system. The CO₂ absorbing solvent 1007absorbing the CO₂ is also called a rich solvent. Pressure is raised forthe rich solvent 1007 by a rich solvent pump 1012, and heated by arich/lean solvent heat exchanger 1013 by the CO₂ absorbing solvent (leansolvent) 1009 regenerated by removing CO₂ in the regeneration column1008 described later, and supplied to the regeneration column 1008.

The rich solvent 1007 released from the upper part of the regenerationcolumn 1008 to the interior of the regeneration column 1008 receivesheat from water vapor generated inside the regeneration column 1008 anda large amount of CO₂ is discharged. The CO₂ absorbing solvent fromwhich a portion or a large amount of CO₂ is released inside theregeneration column 1008 is called a semi-lean solvent. The semi-leansolvent becomes a CO₂ absorbing solvent from which almost all of the CO₂is removed by the time it reaches the lower portion of the regenerationcolumn 1008. The absorbing solvent regenerated by removing almost all ofthe CO₂ is called a lean solvent. A re-boiler 1014 heats the leansolvent by using steam. Meanwhile, CO₂ gas 1015 together with watervapor released from the rich solvent and the semi-lean solvent insidethe regeneration column 1008 is derived from the head top part of theregeneration column 1008, the water vapor is condensed by an overheadcondenser 1016, water is separated by a separation drum 1017, and CO₂gas 1018 is released from the system and collected. The water separatedby the separation drum 1017 is supplied by a condensed-water circulatingpump 1019 to the upper part of regeneration column 1008. The regeneratedCO₂ absorbing solvent (lean solvent) 1009 is cooled by the rich solvent1007 by the rich/lean solvent heat exchanger 1013, which is followed byraising the pressure by a lean solvent pump 1020, and the resultantwater is cooled by a lean solvent cooler 1021, and thereafter suppliedto the CO₂ absorption column 1006.

In FIG. 9, reference numeral 1001 a is a stack flue of the industrialfacility 1001 such as a boiler and a gas turbine, and 1001 b is a stackhaving a damper on the inside. There are cases that the CO₂ collectingdevice is installed after the system is completed to collect CO₂ from anexisting source of the flue gas and cases that it is simultaneouslyattached to a new source of the flue gas.

As the conventional effective utilization of the carbon dioxide in fluegas, some of the carbon dioxide in flue gas is merely collected toproduce carbon dioxide for carbonated drinks and dry ice. However, thegreenhouse effect caused by carbon dioxide is recently pointed out asone of the causes of global warming. Measures are becoming an urgentnecessity internationally to protect the global environment, and also,the source of generating the carbon dioxide affects every field of humanactivity, which burns fossil fuels, and demands of restricting thedischarge tend are becoming even stronger. Along with this tendency, inpower generation facilities such as thermal power stations that use alarge amount of fossil fuels, there have been a method in which flue gasof industrial facilities such as a boiler and a gas turbine is broughtinto contact with a CO₂ absorbing solvent, all of CO₂ in the flue gas isremoved and collected, and a method for storing the collected CO₂without releasing it into the atmosphere.

As described above, in the conventional CO₂ collecting system 1000,there has been proposed that, when collecting all of carbon dioxide influe gas, a containing unit such as a valve or damper that can be openedand closed inside the stack 1001 b, as shown in FIG. 9, is installed toclose and stop during the operation of the CO₂ collecting device and torelease when the operation of the CO₂ collecting device is stopped whilethe source of the flue gas is kept operating.

However, at the time of stopping the operation of the CO₂ collectingdevice, unless an operation such as containment of the valve, damper orthe like, which closes the interior of the stack or releasing is surelyperformed, discharge of flue gas is not performed smoothly, and thereare occasions that the industrial facilities (such as gas turbines) atthe upstream side are adversely affected.

Further, in a turbine facility that generates electricity of 200,000kilowatts in which 3000 ton of carbon dioxide are processed in each day,an amount of discharged flue gas becomes enormous and a stack having,for example, a diameter of 7 to 10 meters is required. Under suchcircumstances, a facility of a containing unit such as a valve and adamper that contains the flue gas needs to be larger.

Accordingly, a system capable of drawing in substantially all of a largeamount of flue gas to a carbon-dioxide collecting device in a simple,stable, and safe manner has been desired.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve theproblems in the conventional technology.

According to an aspect of the present invention, a system for collectingcarbon dioxide in flue gas includes: a stack that discharges flue gasdischarged from an industrial facility to outside; a blower that isinstalled at a downstream side of the stack and draws the flue gastherein; a carbon-dioxide collecting device that collects carbon dioxidein the flue gas drawn in by the blower; and a gas flow sensor that isarranged near an exit side within the stack and measures a gas flowrate. A drawing amount of the flue gas to the carbon-dioxide collectingdevice by the blower is increased until an flow rate of the flue gasfrom the stack becomes zero in the gas flow sensor, and when the flowrate of the flue gas from the stack becomes zero, drawing in any morethan the amount is stopped, and the carbon dioxide in the flue gas iscollected while drawing in the flue gas by a substantially constantamount.

According to another aspect of the present invention, a system forcollecting carbon dioxide in flue gas includes: a stack that dischargesflue gas discharged from an industrial facility to outside; a blowerthat is installed at a downstream side of the stack and draws the fluegas therein; a carbon-dioxide collecting device that collects carbondioxide in the flue gas drawn in by the blower; and a sensor that isarranged at least one location in a stack flue at a downstream side ofthe stack within the stack and measures gas temperature or gas type. Adrawing amount of the flue gas by the blower to the carbon-dioxidecollecting device is increased until the gas temperature or aconcentration of the gas type changes in the sensor, and when the gastemperature or the concentration of the gas type changes, drawing in anymore than the amount is stopped, and the carbon dioxide in the flue gasis collected while drawing in the flue gas by a substantially constantamount.

According to still another aspect of the present invention, a system forcollecting carbon dioxide in flue gas includes: a stack that dischargesflue gas discharged from an industrial facility to outside; a blowerthat is installed at a downstream side of the stack and draws the fluegas therein; a carbon-dioxide collecting device that collects carbondioxide in the flue gas drawn in by the blower; and a plurality ofsensors that are arranged in an stack flue at an upstream side of thestack and at a downstream side of the stack and measure gas temperatureor a concentration of gas type. A drawing amount of the flue gas by theblower to the carbon-dioxide collecting device is increased until adifference in the gas temperature or the concentration of the gas typeis generated, and when the difference is generated, drawing in any morethan the amount is stopped, and the carbon dioxide in the flue gas iscollected while drawing in the flue gas by a substantially constantamount.

In the system for collecting carbon dioxide in flue gas, the gas typemay be oxygen or carbon dioxide.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a system for collecting carbon dioxidein flue gas according to a first embodiment of the present invention;

FIG. 2 depicts a relationship between a discharged amount of flue gasfrom a stack and a drawing amount of flue gas in the first embodiment;

FIG. 3A is a schematic diagram of a system for collecting carbon dioxidein flue gas according to a second embodiment of the present invention;

FIG. 3B is a schematic diagram of another system for collecting carbondioxide in flue gas according to the second embodiment;

FIG. 3C is a schematic diagram of still another system for collectingcarbon dioxide in flue gas according to the second embodiment;

FIG. 4 depicts a relationship between discharged amount of flue gas froma stack and a drawing amount of flue gas in the second embodiment;

FIG. 5A is a schematic diagram of a system for collecting carbon dioxidein flue gas according to a third embodiment of the present invention;

FIG. 5B is a schematic diagram of another system for collecting carbondioxide in flue gas according to the third embodiment;

FIG. 6 depicts a relationship between oxygen concentration from a stackand a drawing amount of flue gas in the third embodiment;

FIG. 7A is a schematic diagram of a system for collecting carbon dioxidein flue gas according to a fourth embodiment of the present invention;

FIG. 7B is a schematic diagram of another system for collecting carbondioxide in flue gas according to the fourth embodiment;

FIG. 8 depicts a relationship between oxygen concentration of flue gasfrom a stack and a drawing amount of flue gas in the fourth embodiment;and

FIG. 9 is a schematic diagram of a conventional system for collectingcarbon dioxide in flue gas.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is explained below in detail with reference to theaccompanying drawings. The present invention is not limited to theembodiments. In addition, constituent elements in the followingembodiments include elements that readily occur to those skilled in theart or substantially equivalent elements.

A system for collecting carbon dioxide in flue gas according to a firstembodiment of the present invention is explained with reference to thedrawings.

FIG. 1 is a schematic diagram of the system for collecting carbondioxide in flue gas according to the first embodiment.

As shown in FIG. 1, a system for collecting carbon dioxide in flue gas10-1 according to the first embodiment includes a stack 13 thatdischarges flue gas 12 discharged from an industrial facility 11 tooutside, a blower 14 that is installed at the downstream side of thestack 13 and draws the flue gas 12 therein, a carbon-dioxide collectingdevice 15 that collects carbon dioxide in the flue gas 12 drawn in bythe blower 14, and a gas flow sensor S1 arranged near an exit sidewithin the stack 13. In the gas flow sensor S1, a drawing amount of theflue gas 12 by the blower 14 to the carbon-dioxide collecting device 15is increased until an exhaust flow rate of the flue gas from the stack13 becomes zero, and when the discharged amount of flue gas from thestack 13 becomes zero, drawing in any more than that amount is stoppedand the carbon dioxide in the flue gas is collected while the flue gas12 is drawn in by a substantially constant amount.

The carbon-dioxide collecting device 15 is not particularly limited andcan be any device that collects carbon dioxide, similar to the CO₂collecting device shown in the FIG. 9.

In the first embodiment, the exhaust flow rate to the outside of theflue gas 12 from the stack 13 is monitored all the time in the gas flowsensor S1.

When the drawing amount of the flue gas 12 by the blower 14 to thecarbon-dioxide collecting device 15 is increased until the exhaust flowrate from the stack 13 becomes zero, the discharged amount of the fluegas 12 to the outside from the stack declines slowly as shown in FIG. 2.When the discharged amount of flue gas from the stack 13 becomes zero,drawing in any more than that amount by the blower 14 is stopped, andthe carbon dioxide in the flue gas 12 is collected by the carbon-dioxidecollecting device 15 while drawing in the flue gas 12 by the blower 14while maintaining the drawing amount to become approximately zero(substantially constant amount).

Accordingly, all of the flue gas from the industrial facility 11 can bestably drawn into the carbon-dioxide collecting device 15 and all of thecarbon dioxide in flue gas can be collected.

Further, in the carbon-dioxide collecting device 15, since air is mixedin the flue gas which is a target to be processed, malfunctions is notgenerated even when outside atmosphere is drawn into the carbon-dioxidecollecting device 15 from the stack 13.

In the present invention, the industrial facility is not particularlylimited, and examples thereof can include a boiler, a combustionfurnace, and a gas turbine facility, which generate carbon dioxide. Whenthe gas turbine facility is used, a heat recovery steam generator (HRSG)that collects heat having high temperature (about 580° C.) of the fluegas 12 discharged from a gas turbine can be installed.

A system for collecting carbon dioxide in flue gas according to a secondembodiment of the present invention is explained next with reference tothe drawings.

FIG. 3A is a schematic diagram of the system for collecting carbondioxide in flue gas according to the second embodiment.

As shown in FIG. 3A, a system for collecting carbon dioxide in flue gas10-2A according to the second embodiment includes the stack 13 thatdischarges the flue gas 12 discharged from the industrial facility 11 tothe outside, the blower 14 that is installed at the downstream side ofthe stack 13 and draws the flue gas 12 therein, the carbon-dioxidecollecting device 15 that collects carbon dioxide in the flue gas 12drawn in by the blower 14, and a gas temperature sensor S2 arrangedwithin the stack 13. In the gas temperature sensor S2, the drawingamount of the flue gas 12 by the blower 14 to the carbon-dioxidecollecting device 15 is increased until the gas temperature declines,and when the gas temperature declines, drawing in any more than thatamount is stopped and the carbon dioxide in the flue gas is collectedwhile the flue gas 12 is drawn in by a substantially constant amount.

That is, in the gas temperature sensor S2, the exhaust temperature ofthe flue gas to be discharged from the stack 13 to the outside ismonitored all the time by the gas temperature sensor S2.

Even when the drawing amount of the flue gas 12 by the blower 14 to thecarbon-dioxide collecting device 15 is increased, the exhausttemperature from the stack 13 is almost maintained at constanttemperature (100 to 180° C.) up to a certain time point as shown in FIG.4. However, when atmosphere from outside the stack 13 flows in withinthe stack 13, the flue gas 12 is cooled by the atmosphere, and thetemperature declines. Additionally, immediately before the temperaturechange starts (a point indicated by an arrow in FIG. 4), drawing in theflue gas 12 by the blower 14 any more than that amount is stopped, andthe carbon dioxide in the flue gas 12 is collected by the carbon-dioxidecollecting device 15 while drawing in the flue gas 12 by the blower 14while maintaining the stopped drawing amount (substantially constantamount).

Accordingly, all of the flue gas from the industrial facility 11 can bestably drawn into the carbon-dioxide collecting device 15 and all of thecarbon dioxide in flue gas can be collected.

FIG. 3B depicts another system for collecting carbon dioxide in flue gas10-2B according to the second embodiment. A gas temperature sensor S3 isarranged before the blower 14 at the downstream side of the stack, andsimilarly, the gas temperature is measured and the flue gas is drawn in.

By using the gas temperature sensor S3 to control the drawing amountwhile monitoring the gas temperature in the same way as the gastemperature sensor S2, all of the flue gas from the industrial facility11 can be stably drawn into the carbon-dioxide collecting device 15 andall of the carbon dioxide in the flue gas can be collected.

FIG. 3C depicts still another system for collecting carbon dioxide influe gas 10-2C according to the second embodiment. The gas temperaturesensor S3 is arranged before the blower 14 and at the downstream side ofthe stack 13, and a gas temperature sensor S4 also is arranged within astack flue at the upstream of the stack 13.

In the gas temperature sensors S3 and S4, the drawing amount of the fluegas 12 by the blower 14 to the carbon-dioxide collecting device 15 isincreased until a difference in the flue gas temperature is generated,and when the difference in the gas temperatures is generated, drawing inany more than that amount is stopped and the carbon dioxide in flue gasis collected while drawing in the flue gas by a substantially constantamount.

Accordingly, all of the flue gas from the industrial facility 11 can bestably drawn into the carbon-dioxide collecting device 15.

A system for collecting carbon dioxide in flue gas according to a thirdembodiment of the present invention is explained next with reference tothe drawings.

FIG. 5A is a schematic diagram of the system for collecting carbondioxide in flue gas according to the third embodiment.

As shown in FIG. 5A, a system for collecting carbon dioxide in flue gas10-3A according to the third embodiment includes the stack 13 thatdischarges the flue gas 12 discharged from the industrial facility 11 tothe outside, the blower 14 that is installed at the downstream side ofthe stack 13 and draws the flue gas 12 therein, the carbon-dioxidecollecting device 15 that collects carbon dioxide in the flue gas 12drawn in by the blower 14, and an O₂ sensor S5 arranged within the stack13. In the O₂ sensor S5, the drawing amount of the flue gas 12 by theblower 14 to the carbon-dioxide collecting device 15 is increased untilthe oxygen gas concentration is raised, and when the oxygen gasconcentration is raised, drawing in any more than that amount is stoppedand the carbon dioxide in the flue gas 12 is collected while the fluegas 12 is drawn in by a substantially constant amount.

That is, in the O₂ sensor S5, the O₂ sensor S5 monitors all the time theoxygen concentration of the flue gas to be discharged from the stack 13to the outside.

Even when the drawing amount of the flue gas 12 by the blower 14 to thecarbon-dioxide collecting device 15 is increased, the oxygenconcentration of flue gas from the stack is maintained almost atconstant (in a case of the flue gas from a boiler, it is 2 to 5%, and ina case of the flue gas from a gas turbine, it is 12 to 15%) up to acertain time point as shown in FIG. 6. However, when atmosphere fromoutside of the stack 13 flows into the stack, oxygen in the atmosphereis mixed in the flue gas 12, and the oxygen concentration is raised.Immediately before the concentration change in oxygen starts (a pointindicated by an arrow in FIG. 6), drawing in any more flue gas 12 by theblower 14 is stopped, and carbon dioxide in the flue gas 12 is collectedby the carbon-dioxide collecting device 15 while drawing in the flue gas12 by the blower 14, maintaining the stopped drawing amount(substantially constant amount) at the same time.

Accordingly, all of the flue gas from the industrial facility 11 can bestably drawn into the carbon-dioxide collecting device 15 and all of thecarbon dioxide in flue gas can be collected.

In FIG. 5A, an O₂ sensor S6 is installed at the upstream side of theblower 14 at the downstream side of the stack 13, and the oxygenconcentration can be measured by the O₂ sensor S6 instead of the O₂sensor S5. At this time, the O₂ sensor S5 can be used together so thatthe oxygen concentration can be measured by the both sensors S5 and S6.

FIG. 5B depicts another system for collecting carbon dioxide in flue gas10-3B according to the third embodiment. An O₂ sensor S6 is arranged atthe downstream side of the stack 13 and before the blower 14, and an O₂sensor S7 is also arranged within the stack flue at the upstream of thestack 13.

In the O₂ sensors S6 and S7, the drawing amount of the flue gas 12 bythe blower 14 to the carbon-dioxide collecting device 15 is increaseduntil a difference in the oxygen concentration in the flue gas isgenerated, and when the difference in the oxygen concentration isgenerated, drawing in any more than that amount is stopped and carbondioxide in the flue gas is collected while drawing in the flue gas by asubstantially constant amount.

Accordingly, all of the flue gas from the industrial facility 11 can bestably drawn into the carbon-dioxide collecting device 15.

A system for collecting carbon dioxide in flue gas according to a fourthembodiment of the present invention is explained next with reference tothe drawings.

FIG. 7A is a schematic diagram of the system for collecting carbondioxide in flue gas according to the fourth embodiment.

As shown in FIG. 7A, a system for collecting carbon dioxide in flue gas10-4A according to the fourth embodiment includes the stack 13 thatdischarges the flue gas 12 discharged from the industrial facility 11 tothe outside, the blower 14 that is installed at the downstream side ofthe stack 13 and draws the flue gas 12 therein, the carbon-dioxidecollecting device 15 that collects carbon dioxide in the flue gas 12drawn in by the blower 14, and a CO₂ sensor S8 arranged within the stack13. In the CO₂ sensor S8, the drawing amount of the flue gas 12 drawn inby the blower 14 to the carbon-dioxide collecting device 15 is increaseduntil the carbon dioxide gas concentration is raised, and when thecarbon dioxide gas concentration is raised, drawing in any more thanthat amount is stopped, and the carbon dioxide in the flue gas iscollected while the flue gas is drawn in by a substantially constantamount.

That is, in the CO₂ sensor S8, the CO₂ sensor S8 monitors all the timethe carbon dioxide concentration of the flue gas to be discharged fromthe stack 13 to the outside.

Even when the drawing amount of the flue gas 12 by the blower 14 to thecarbon-dioxide collecting device 15 is increased, the carbon dioxideconcentration of flue gas from the stack is maintained almost atconstant (in a case of the flue gas from a boiler, it is 8 to 14% and ina case of the flue gas from a gas turbine, it is 3.5 to 4%) up to acertain time point as shown in FIG. 6. However, when atmosphere flows inthe stack from outside of the stack 13, carbon dioxide in the atmosphereis mixed in the flue gas 12, and the carbon dioxide concentration israised. Immediately before the concentration change of the carbondioxide starts (a point indicated by an arrow in FIG. 8), drawing in anymore flue gas 12 by the blower 14 is stopped, and the carbon dioxide inthe flue gas 12 is collected by the carbon-dioxide collecting device 15while drawing in the flue gas 12 by the blower 14 while maintaining thestopped drawing amount (substantially constant amount).

Accordingly, all of the flue gas from the industrial facility 11 can bestably drawn into the carbon-dioxide collecting device 15 and all of thecarbon dioxide in flue gas can be collected.

In FIG. 7A, a CO₂ sensor S9 is installed at the upstream side of theblower 14 at the downstream side of the stack 13, and the carbon dioxideconcentration can be measured by the CO₂ sensor S9 instead of the CO₂sensor S8. At this time, the CO₂ sensor S8 can be used together so thatthe oxygen concentration can be measured by both the sensors S8 and S9.

FIG. 7B depicts another system for collecting carbon dioxide in flue gas10-4B according to the fourth embodiment. The CO₂ sensor S9 is arrangedat the downstream side of the stack 13 and before the blower 14, and aCO₂ sensor S10 is also arranged in the stack flue at the upstream of thestack 13.

In the CO₂ sensors S9 and S10, the drawing amount of the flue gas 12 bythe blower 14 to the carbon-dioxide collecting device 15 is increaseduntil a difference in the carbon dioxide concentration in the flue gasis generated, and when the difference in the carbon dioxideconcentration is generated, drawing in any more than that amount isstopped, and the carbon dioxide in flue gas is collected while drawingin the flue gas by a substantially constant amount.

Accordingly, all of the flue gas from the industrial facility 11 can bestably drawn into the carbon-dioxide collecting device 15.

To achieve more accurate control, the first to fourth embodiments can beappropriately combined to use a plurality of different sensors and toperform the control.

According to the present invention, substantially all of a large amountof flue gas can be drawn into a carbon-dioxide collecting device with asimple facility and in a stable and safe manner.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

What is claimed is:
 1. A system for collecting carbon dioxide in fluegas, comprising: a stack that discharges flue gas discharged from anindustrial facility to outside; a blower that is installed at adownstream side of the stack and draws the flue gas therein; acarbon-dioxide collecting device that collects carbon dioxide in theflue gas drawn in by the blower; and a plurality of sensors that arearranged in an stack flue at an upstream side of the stack and at adownstream side of the stack and measure gas temperature or aconcentration of gas type, wherein a drawing amount of the flue gas bythe blower to the carbon-dioxide collecting device is increased until adifference in the gas temperature or the concentration of the gas typeis generated, and when the difference is generated, drawing in any morethan the amount is stopped, and the carbon dioxide in the flue gas iscollected while drawing in the flue gas by a substantially constantamount.